1. Field of the Invention
The present invention relates to a terminal apparatus for use with an image communication system such as a cable TV system.
2. Description of the Related Art
In conventional TV broadcasting systems and cable TV systems (CATV), image signals that are transmitted from broadcasting stations are analogue signals. On the other hand, digital CATV systems that transmit digital image signals have been proposed. An example of CATV system is disclosed in U.S. Pat. No. 5,191,410. The digital CATV systems have been accomplished by the use of highly efficient coding techniques such as DCT (Discrete Cosine Transform) techniques along with improvement of transmission lines and construction of communication network. In other words, with the band for one channel of convention analog image signals, compressed image signals of approximately 10 channels can be transmitted.
The digital CATV systems, which receive and transmit digital image signals, can provide various services and data transmission for not only conventional TV images, but home shopping (electronic mall and electronic banking) and TV games. As various services are provided, information supplied by providers will be specialized.
In such a digital CATV system, even if the data rate of digital signals that are transmitted is constant, depending on the contents of programs, the data rate may vary, program by program. For example, images used for data retrieval are not transmitted as image data with relatively high compression rate and relatively low data rate. On the other hand, when detail information is required for images, the data rate thereof should be high. For still images, the data compression rate can be increased and thereby the data rate can be decreased. In addition, due to various reasons, image data with various data rates may be transmitted.
In the digital image communication systems as with the digital CATV systems, image storage devices are preferably disposed in receiving terminal apparatuses. This is because while the user sees a TV program, since other TV programs can be stored in the image storage device, the user can see the stored programs in his free time. Since digital image signals are stored, the image storage device is preferably a digital cassette tape recorder, a hard disk, a flexible disk, a semiconductor memory, or the like.
The digital cassette tape recorder (hereinafter referred to as digital VCR) performs parity code adding process with error correction code, formatting process, and modulating process and so forth for video signals that have been highly efficiently coded. Thereafter, with a rotating head of the digital cassette tape recorder records the digital video signals on a magnetic tape. In addition, the digital cassette tape recorder performs demodulating process, format decomposing process, error correcting process, and so forth for the signals recorded on the magnetic tape so as to reproduce the digital video signals. Examples of the digital VCR are set forth in EP-A-0553817 and 0574889. In the digital CATV system, when the digital VCR is used as a data storage device, the general data and the continuous data are recorded on the same tape depending on the user's selection or in the received order. However, the general data should be more quickly accessed than the continuous data. If the general data is intermittently recorded on the tape, the data cannot be easily accessed.
In addition, the hardware of the process for the general data is preferably shared with the hardware of the process for the continuous data. For example, the error correction code encoding process, the frame segmenting process that defines the format of data recorded on the tape, and so forth are preferably shared. When such a digital VCR is used for the image storage apparatus, data with variable data rates lower than standard data rate should be recorded and reproduced without wasting the magnetic tape.
In addition, in the digital CATV system, data in which a plurality of program channels have been time-division multiplexed is transmitted. Normally, one of the program channels is selected by a home terminal apparatus so as to see or store the program. However, other program channels cannot be used later.